The thesis is concerned with the synthesis, characterisation and reactivity of a variety of nickel(II) diphosphine complexes considered possible catalyst precursors for the copolymerisation of CO and ethene. [Ni(diphos)(o-tolyl)(py)]Y (1), [Ni(diphos)(_2)](Y)(_2) (2), and [Ni(diphos)(S)(_2)](Y)(_2) (3) {Y = OTs, OTf} are found to be catalyst precursors for the CO/ethene reaction (115 C, 1200psi, 1:1 CO: ethene) with high selectivity to polyketone formation, the activity depending on the phosphine ligand employed. However, the activity is low and attributed in part to the formation of the [Ni(diphos)(CO)(_2)] (4) complexes which are stable under the reaction conditions. The diphosphine hgand employed, particularly the nature of the backbone, is found to influence the synthesis and reaction chemistry of the complexes (1), (2) and (3).A series of complexes of the type [Ni(R(_2)P(CH(_2))(_a)PR(_2))(o-tolyl)Br] (5) {n = 2; R = Ph, Cy, 'Bu) have been synthesised and the complex [Ni(dppe)(o-tolyl)Cl] has been characterised by X-ray crystaliography. The influence of the chelating diphosphine on the structural characteristics and NMR parameters of these compounds has been investigated. When n > 2 the complexes of the type [Ni(diphos)(o-tolyl)X] were not isolated. The reaction of type (5) complexes with TIY (Y = OTs, BF(_4)) in pyridine led to the formation of complexes of the type [Ni(diphos)(o-tolyl)(py)]Y (1).A series of complexes of the type [Ni(diphos)Cl(_2)] (6) {diphos = dope, dBpe, dcpn} have been synthesised and characterised by X-ray crystallography. The influence of the chelating phosphine ligand on structural characteristics of these compounds has been investigated. Complexes of the type (2) and (3) can be synthesised from type (6) complexes. Detailed studies on the behaviour of a series of complexes of the type [Ni(diphos)(_2)](Y)(_2) (2) and [Ni(diphos)(Y)(_2)] (3) {Y = OTs and OTf), and the equilibrium between them in solution have been undertaken. The complex [Ni(dppe)(-2)](OTs)(_2) has been characterised by X-ray crystallography.

Several new group 13, 14 and 15 derivatives with the ligands 2,4,6-(CF(_3))(_3)C(_6)H(_2) (Ar), 2,6- (CF(_3))(_2)C(_6)H(_3) (Ar') and / or 2,4-(CF(_3))(_2)C(_6)H(_3) (Ar") have been prepared. They have been characterised by multinuclear NMR spectroscopy and, for all isolated compounds, by elemental analysis and, where possible, single crystal X-ray diffraction. Reaction of ArLi or the mixture Ar'Li/Ar"Li with BCI3 has led to the characterisation of several mono- and disubstituted compounds, but attempted substitution in AICI3 was unsuccessful. Reaction of EC1(_4) (E = Si, Ge, Sn) with the Ar'Li/Ar"Li mixture yielded predominantly the less sterically hindered disubstituted product Ar"(_2)ECl(_2) for E = Si and Ge but to Ar'(_2)ECl(_2) for E = Sn. In the case of B or Si, chlorine exchange is observed and Ar(_2)BF, Ar(_2)SiF(_2) and Ar'(_2)SiF(_2) have been synthesised. Ar(_2)SiF(_2) is the only product identified in the reaction of ArLi with SiC1(_4). Reaction of ArLi or the Ar'Li/Ar"Li mixture, in an appropriate ratio, with group 15 derivatives gave rise to several mono-or disubstituted compounds of the type ArEX(_2), Ar(_2)EX, Ar'EX(_2), Ar"EX(_2), Ar"(_2)EX and Ar'Ar"EX (E = P or As; X = H, CI or Br). (^19)F NMR spectra of Ar'Ar"EX show that, for the two ortho-CF(_3) groups of the Ar' moiety, there is free rotation of the aryl group around the central atom. A series of variable temperature studies has been carried out, and allowed the determination of the rotational energy barrier of the molecule. For the first time, the molecular structures of derivatives containing three fluoroxyl ligands have been determined (Ar"(_3)B and Ar'Ar"(_2)Sb).The synthesis of some new platinum complexes has been facilitated by reaction of phosphanes with the platinum dimer [(PtCl(_2)(Pet(_3))](_2) or [(PtBr(_2)(Pet(_3))](_2). Reactions of the platinum dimer with arsane derivatives have not been successful. Halogen exchange was observed between bromophosphane ligands and CI groups on the platinum. Attempts have been made to synthesise new P=E derivatives containing the electron- withdrawing substituents Ar or Ar' via reaction with the chlorine abstractor W(PMe(_3))(_6)- ArP=PAr and Ar'P=PAr' have been prepared. Synthesis of the first phosphaalkyne containing Ar or Ar' has been attempted by reacting a phosphaalkene with a Pt(0) species.

An alkylphosphinate is an attractive isostere for a carboxylate. The acid is more acidic than a carboxylic acid, is amenable to (^31)P NMR analysis and is subject to easy structural modification by variation of the phosphorus alkyl or aryl substituent. Amino acid complexing agents incorporating carboxymethyl groups are ubiquitous, but the corresponding phosphinic acid analogues have been much less studied. On chelation of a metal ion to a ligand nitrogen and a phosphorus oxygen atom, a new stereogenic centre at phosphorus is created. In polydentate ligands diastereoisomeric complexes may form. A new family of acyclic ligands with phosphinic acid binding groups have been synthesised. The protonation constants have been determined and used for the determination of the stability constants for a range of metal complexes. A complexing agent based on a 9N(_3) macrocyclic skeleton incorporating pendant arm phosphinic acid donors, provides an octahedral site for metal complexation. The structures of seven complexes with a ligand of this type, have been determined by X-ray crystallography. They fall into two groups, those with a C(_3) axis (Cu (II), Co (II), Zn (II) and Ni (II)) and those with an approximate C(_3) axis (Ga (III), Fe (III) and In (III)).

D.Sc. / Please view full text to see abstract

The mono protection of 1,4,7-triazacyclononane ([9]-aneN₃) was accomplished efficiently through the formation of an orthoamide derivative. The orthoamide was used to form three mono protected derivatives of [9]-aneN₃ which contained either a formyl, methyl, or benzyl protecting group attached to one of the nitrogen donors. The macrobicyclic complexes bicycloN₅, Me-bicycloN₅, and Bz-bicycloN₅ were synthesized through the Michael addition of two functional arms to the mono protected derivatives of [9]-aneN₃ followed by a ring closure template reaction around copper with glyoxal. Incomplete reduction by BH₃ THF led to the isolation of an enamine intermediate. The solution behavior o f the Ni(II) and Ni(III) complexes of these macrobicyclic ligands is presented. The methyl and benzyl derivatives were found to have similar abilities as the parent bicycloN₅ ligand to stabilize the Ni(III) metal ion. Removal of the benzyl protecting group was achieved by reaction with formic acid in the presence of a Pd/C catalyst. Attempts to couple two mono protected nonane molecules through the addition of functional acid chloride arms under conditions of high dilution were unsuccessful. Reaction of the benzyl protected bicyclic ligand Bz-bicycloN₅ with a bridging ligand in a high dilution reaction did provide evidence for the formation of a small amount of the novel macrotricyclic ligand tricyclo[9.14.9]N₆. The Ni(II) complexes of the macrobicyclic ligands, and a series of other macrocyclic and related Ni(II) complexes having varying NiIII/II redox potentials, were used to study the quenching of the excited state of the platinum(II) dimeric complex Pt₂(pop)₄⁴− . The quenching rate constants kq were determined, and quenching of the excited state *Pt₂(pop)₄⁴− by the nickel complexes was found to proceed by reductive electron transfer. These results are discussed in terms of Marcus Theory. A plot of logkq versus the ΔG for electron transfer was found to exhibit classic Rehm- Weller behavior. The excited state potential Pt₂(pop)₄⁴⁻*/⁵- was estimated from this series of quenching reactions and a range of 1.24 to 1.34 V (vs. NHE) was identified. The photochemical and photophysical properties of the macrocyclic complex Cr([18]-aneN₆)³+ ([18]-aneN₆ = 1,4,7,10,13,16-hexaazacyclooctadecane) were investigated and compared to the properties of the photoreactive Cr(III) complex Cr(sen)³+ (sen = 4,4',4"-ethylidynetris(3-azabutan-l-amine)). The complex Cr([18]- aneN₆)³+ was found to be unreactive (Ørxn < 10⁻³) while the photoreactivity of Cr(sen)³+ was confirmed (Ørxn = 0.10). Both of these complexes have very short ambient ²E emission lifetimes and this is discussed in terms of distortions imposed on the complexes by the coordination of the ligands. Direct irradiation into the doublet excited state of Cr(sen)3⁺ at 675 nm resulted in a decrease in the quantum yield for the photoreaction of this complex from Ørxn=0.10 for quartet irradiation to Ørxn=0.08 for doublet irradiation. A model is suggested in which there are two competitive processes deactivating the doublet excited state; reverse intersystem crossing to the lowest quartet excited state and nonradiative decay back to the ground state. The temperature dependence of the ²E emission lifetime was fitted to a two-term Arrhenius function to give estimates for the pre-exponential factors and activation energies of these two deactivation processes. Values of A₁ = (1.2 ± 0.9) x 1O¹⁵ s⁻¹ and Eₐ₁ = 45 ± 1 kJ mol⁻¹,and A₂ = (5.4 ± 1.2) x 10¹¹s⁻¹ and Eₐ2 = 29 ± 1 kJ mol⁻¹ were obtained. The photostereochemistry of Cr(sen)³⁺ was investigated using a modified reversed phase HPLC technique. A total of four photoproducts were identified from the photolysis of the resolved stereoisomers of Cr(sen)³⁺ and a loss of optical activity was found to be associated with the photoreaction. These results are discussed in terms of current models for predicting photostereoreactivity of Cr(III) complexes. / Graduate

A Dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science. / The addition of cyclohexyl substituents to existing ligands was investigated for its potential use as a factor in ligand design for achieving high specificity for particular metal ions, (Abbreviation abstract) / AC 2018

Thesis advisor: Kian L. Tan / Chapter 1. The use of directing groups is a powerful way to control selectivity in organic chemistry. Due to their ability to install new functionality in a reliable fashion, directing groups have had a profound impact on stereoselective, site-selective, and regioselective transformations. More recently, catalytic directing groups have been developed and utilized in a variety of metal-catalyzed transformations, including C-H activation and hydroacylation, and have the potential to be more broadly applied to other transformations. Chapter 2. Catalytic directing groups have recently been designed for hydroformylation. Based on the design of racemic scaffolding ligand 2.5, enantioenriched ligand 2.42 was synthesized for the asymmetric hydroformylation of para-methoxyphenyl (PMP) protected allylic amines. Under mild conditions, a variety of 1,2-disubstituted olefins underwent directed hydroformylation to afford the proximal &#946;-amino alcohol products in good yields and excellent enantioselectivities. The substrate scope has been extended to electronically modified allylic anilines. A modest resonance effect was seen upon the aniline substrate binding to the ligand, which, in turn, manifested in the hydroformylation reaction results. Thus the first enantioselective reaction performed with a catalytic directing group was demonstrated. Chapter 3. Ligand 3.67 was developed, which promotes aldehyde formation on the distal olefinic carbon relative to the directing functionality on the substrate. This is in contrast to other phosphorus-based directing groups that have been successful at placing the aldehyde on the proximal olefinic carbon. Ligand 3.67 has been applied to the diastereoselective hydroformylation of homoallylic alcohols to afford &#948;-lactones selectively. Altering the distance between the alcohol and olefin revealed that homoallylic alcohols afford the distal lactone with the highest levels of regioselectivity. Taken together with previous examples of proximal-selective hydroformylation, these results being to more fully address the challenge of controlling regioselectivity in hydroformylation. Chapter 4. The harvesting of energy from light to power chemical transformations is an underdeveloped area. Utilizing p-type silicon nanowires (SiNWs) as a photocathode, the photoelectrochemical carboxylation of aromatic ketones has been developed to afford &#945;-hydroxy carboxylic acids. Utilizing low operating potentials, the direct reduction of carbon dioxide (CO2) is avoided. Highlighting the synthetic utility of this transformation, two precursors to the NSAID compounds ibuprofen and naproxen were synthesized using CO2, and abundant C1 feedstock, and light, a crucial source of energy in nature. / Thesis (PhD) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment of the requirements for the degree of Doctor of Philosophy, Johannesburg, 1996 / The glutathione S-transferases (GST) are a supergene family of h0111o-or heterodimeric Phase II detoxification enzymes which catalyse the S-conjugation between glutathione and an electrophilic substrate. The active site can be divided into two adjacent functional regions; a highly specific Gssite for binding the physiological substrate glutathione and a nonspecific If-site for binding nonpolar electrophilic substrates. Unfolding of porcine class Pi isoenzyme (pGSTPl~l) was monitored under equilibrium conditions using different physicochemical parameters. The coincidence of unfolding curves obtained with functional and structural probes, the absence of thermodynamically stable intermediates such as a folded monomer, and the dependence of pGSTPl··l stability upon protein concentration, indicate a cooperative and concerted two-state unfolding transition between native dimeric pGSTPl-l and unfolded monomeric enzyme. Equilibrium and kinetic unfolding experiments employing tryptophan fluorescence and enzyme activity measurements were preformed to study the effect of ligand binding to the G-site on the unfolding and stability of the porcine class pi glutathione S-transferase against urea. The presence of glutathione caused a shift in the equilibrium-unfolding curves towards lower urea concentrations and enhanced the first-order rate constant for unfolding suggesting a destabilisation of the pGSTPl-l structure against urea. The presence of either glutathione sulphonate or S-hexylglutathione, however, produced the opposite effect in that their binding to the G-site appeared to exert a stabilising effect against urea. The binding of these glutathione analogues also reduced significantly the degree of cooperativity of unfolding indicating a possible change in the protein's unfolding pathway. / MT2017

Thesis. 1977. Ph.D.--Massachusetts Institute of Technology. Dept. of Chemistry. / M̲i̲c̲ṟo̲f̲i̲c̲ẖe̲ c̲o̲p̲y̲ a̲v̲a̲i̲ḻa̲ḇḻe̲ i̲ṉ A̲ṟc̲ẖi̲v̲e̲s̲ a̲ṉḏ S̲c̲i̲e̲ṉc̲e̲. / Vita. / Includes bibliographical references. / Ph.D.

by Man Kin Tse. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.